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Cubic Diophantine (Posted on 2024-04-18) Difficulty: 3 of 5
Find six distinct positive integers A, B, C, D, E, F, G satisfying:
 A3 + B3 = C3 + D3 = E3 + F3 = 19G3.
Please submit primitive solutions only, that is, A, B, C, D, E, F, G should not have a common factor.

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

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Solution Computer solution Comment 2 of 2 |
A B C D E F G
70  560  198   552   315  525    210

Program output:
{210: [[70, 560], [198, 552], [315, 525]]}

If the variable "big" is increased by a factor of 10, there are 16 more solutions, but they are multiples of the above solution by a factor of 2,3,4, ... etc.
-----------
big = 1000

cubes = [a**3 for a in range(1,big+1)]
lessbig = 1 + int((2*cubes[-1]/19)**(1/3))
if big < 7:
    lessbig += 1
targets = [19 * a**3 for a in range(1,lessbig)]

targetDict = {}
from itertools import combinations
for c in combinations(cubes,2):
    if c[0] + c[1] not in targets:
        continue
    g = round(((c[0] + c[1]) / 19)**(1/3))
    if g not in targetDict:
        targetDict[g] = [[min(c),max(c)]]
    else:
        if [min(c),max(c)] in targetDict[g]:
            continue
        targetDict[g].append([min(c),max(c)])

atleast3 = {}
for key,val in targetDict.items():
    if len(targetDict[key]) < 3:
        continue
    atleast3[key] = val

roots = {}
for k,v in atleast3.items():
    roots[k] = []
    for pair in v:
        cbrts = [round(pair[0]**(1/3)) , round(pair[1]**(1/3))]
        roots[k].append(cbrts)

print(roots)

  Posted by Larry on 2024-04-18 09:38:23
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